This invention relates to an improvement on the method of manufacturing a lateral transistor. A lateral PNP transistor has been produced, for example, by the following steps. First, an N type silicon layer is deposited on a P type semiconductor substrate. The N type silicon layer is divided into a plurality of N type islands by a P type element-isolating region. A thick oxide layer is mounted on part of an element-isolating region and an island. A thin oxide layer is laid in that part of the island on which the silicon layer is exposed. An annular resist pattern is deposited on the thin oxide layer.
A P type impurity is ion implanted into an N type base region through the thin oxide layer. At this time, the resist pattern is used as a mark. The resist pattern is removed. The implanted ion is activated. As a result, an emitter region is formed on that part of the silicon layer which corresponds to the hollow portion of the annular resist pattern. At this time, an annular collector region is formed on that part of the silicon layer which is defined between the outer peripheral wall of the resist pattern and the inner peripheral wall of the thick oxide layer. As a result, an annular region lying between the emitter and collector regions is converted into a base region. A resist pattern is mounted on the thin oxide layer. The resist pattern has an opening formed in that part thereof which faces the part in which a bare leadout region is to be formed. An N type impurity is ion implanted into a silicon layer (base region) through a thin oxide layer with the resist pattern used as a mask. The resist pattern is removed. As a result, the implanted ion is activated to provide a base electrode leadout region.
A CVD-SiO.sub.2 layer is deposited over the whole surface of the resultant structure. The CVD-SiO.sub.2 layer and thin oxide layer are selectively etched. This etching process provides a base electrode leadout contact hole, an emitter electrode leadout contact hole, and a collector electrode leadout contact hole. An aluminium layer is deposited over the whole surface of the resultant structure. The aluminium layer is patterned, thereby providing a base electrode, an emitter electrode and a collector electrode. These electrodes are connected to the corresponding base electrode leadout region, emitter electrode leadout region, and collector electrode leadout region. Hitherto a lateral PNP transistor has generally been fabricated in the above-mentioned manner. One of such manufacturing methods is disclosed, for example, in Japanese patent publication No. Sho 41-5656 (priority claim No. 284611 filed in U.S.A. on May 31, 1963).
With the lateral type PNP transistor, the magnitude of collector electrode is proportional to the effective area of the emitter region. In other words, the magnitude of the collector current is proportional to the peripheral length of the emitter region. On the other hand, the base current flows toward the bottom of the emitter region. Therefore, the base current increases with a rise in the area of the emitter region. To elevate current gain (or amplitude), therefore, it is necessary not only to narrow the base width, but to reduce the real area of the emitter region and to enlarge a ratio between the effective area of the emitter region (or its peripheral length) and the real area of the emitter region.
In the above-mentioned lateral transistor-manufacturing method, the deposition of the emitter and collector regions, and the boring of the emitter electrode leadout contact hole are carried out by applying different resist patterns. In the manufacture of the subject lateral transistor, therefore, it is necessary to take into account the difficulties which might occur in matching the different resist patterns used in masks. Now let it be assumed that an annular resist pattern is formed having a small hollow area to provide a small emitter region. In this case, if a resist used for the selective etching of a layer (for example, CVD-SiO.sub.2) fails to be masked with high precision, the resultant emitter electrode contact hole will spread over an area including the emitter and base regions. In such case, the emitter and base regions are short circuited by the emitter electrode. To suppress the occurrence of short circuiting between the emitter and base regions, it is necessary to expand the emitter region and provide a sufficient margin for masking. In the conventional method of manufacturing a lateral transistor, therefore, a limitation was imposed on the noticeable dimensional reduction of the area of the emitter region, thus presenting difficulties in dense integration of transistors and the manufacture of a transistor ensuring a high current gain.